Many parameters of electronic devices, such as sensors that measure environment variables, are temperature dependent. For example, bandgap voltage references have up to 50 ppm/° C. temperature dependence, operational amplifier input offset voltages drift may be up to 20 μV/° C., and quartz frequency references may have 10-20 ppm/° C. frequency drift. In most cases, the temperature dependence or drifting due to temperature is not linear.
To improve initial accuracy of electronic devices, a single-temperature trim or adjustment of at least one parameter is performed at room temperature, such as 27° C.
A technique employed to eliminate the first-order (linear part) of the temperature drift is described in U.S. Pat. No. 6,614,305. By this method, the output parameter is trimmed at a first temperature, for example, 100° C., to a target level using a variety of techniques such as laser resistor trimming or link cut. In addition, a temperature-dependent variable, such as the difference between current that is proportional to absolute temperature (PTAT) and current that is complementary to absolute temperature (CTAT) is trimmed to zero.
At a second temperature, for example, 20° C., the temperature-dependent variable is used to trim a parameter of interest to a target specification. This trimming does not change the output at the first temperature because this variable was previously trimmed to zero. As a result, the linear temperature dependence of the parameter of interest is eliminated or reduced.
These temperature compensation methods do not compensate for nonlinear fluctuations due to temperature. These nonlinear fluctuations become significant as more precise output parameters are required.